The present invention relates to a method of establishing and/or operating a bore well in a bed or floor under a body of water by means of a drilling barge having a derrick and associated drilling equipment. Such drilling barges may be used for drilling in shallow and calm water areas, such as shallow lakes, river mouths etc. When a drilling barge is to be moved from one drilling site to another distant location it can not be moved over rough waters.
The present invention provides a method, which may improve the usability of a drilling barge. Thus, the present invention provides a method of establishing and/or operating a bore well in a bed or floor under a body of water by means of a drilling barge having a derrick and associated drilling equipment, said method comprising: arranging the drilling barge on top of another, larger floatable vessel, moving the floatable vessel to a location of operation, and anchoring the drilling barge in relation to a bed under said body of water so as to substantially align the derrick with an existing or planned bore well.
By using the method according to the invention an existing drilling barge may be made more versatile. While the existing drilling equipment and auxiliary equipment on the drilling barge may be fully utilised, the larger vessel on which the barge is arranged may lift the derrick to an elevated position, whereby also existing bore wells extending downwards from a platform positioned well above the water surface may be serviced and operated. Furthermore, because the drilling barge is arranged on top of a relatively large vessel anchored to the seabed or sea floor, the drilling barge may be used also in less calm and deeper areas than if the barge had been used separately. Finally, the larger vessel carrying the drilling barge may be used as a means of transportation, which is more resistant to less favourable weather conditions than the drilling barge in itself.
The drilling barge may be positioned on the other floatable vessel in any known manner, for example by means of a stationary or floating crane. However, according to the invention the arranging step may include submerging at least one end of the larger vessel, towing the drilling barge into a desired position in relation to the larger vessel, and raising the submerged end of the larger vessel so as bring the deck of the larger vessel into contact with the bottom of the drilling barge and to lift the drilling barge out of the water.
The larger vessel may be submerged and later raised by pumping water into and out from selected water tanks or chambers contained in the larger supporting vessel. Therefore, the drilling barge may be positioned on top of the other vessel, such as a larger barge or another ship, exclusively by means present on the larger vessel. It is possible to submerge the whole supporting vessel. However, it is more preferred to submerge only the end of the vessel on which the drilling barge should be positioned. Thus, the stern of the larger vessel may be submerged and the drilling barge may thereafter be towed into the said position by towing means arranged on the larger vessel. The towing means may, for example, be a winch with a wire, which may be connected to the stem of the drilling barge. The drilling barge is preferably towed or pulled to a position in which the major part is supported on the deck of the larger vessel, while the part of the drilling barge carrying the derrick and other drilling equipment extends beyond the stern of the larger supporting vessel.
The larger vessel carrying the drilling barge may be floating when the equipment on the drilling barge is operating for drilling a bore hole or bore well in the sea floor or for operating or servicing an existing bore well. In such case the anchoring of the drilling barge includes anchoring of the larger vessel in relation to the bed under the body of water, the drilling barge being fastened immovably in relation to the vessel. The larger floatable vessel may be anchored to the sea floor by mooring lines or other known anchoring means. Such anchoring means may be of the quick-release type such that the drilling vessel may be released quickly if required due to weather conditions or for other reasons. However, alternatively or additionally anchoring may be obtained by submerging the larger vessel so as to position the vessel in contact with said bed, whereby a very stable positioning of the vessel in relation to the sea floor may be obtained.
In order to allow selective adjustment of the height of the lower end of the derrick in relation to the water surface or existing bore well installations supporting spacing means may be arranged between the drilling barge and the larger vessel, so as to position the drilling barge and the drilling equipment thereon in a desired position in relation to the bed or installation. Such spacing means may be replaceable spacing members. In the preferred embodiment, however, the spacing means may comprise hydraulic rams for adjusting the height of the drilling barge and of the derrick positioned thereon.
The drilling barge occupies only a minor part of the deck space of he larger vessel. Therefore, a crane may be positioned on the deck of the larger vessel and may be used for preparing the drilling site, such as for replacing damaged or defective parts of bore well installations.
Even though the main purpose of the larger vessel is to support the drilling barge it may also be used for transporting the drilling barge from one location to a distant second location or drilling site. Because the larger vessel is more seaworthy than the drilling barge the combined vessel may be towed over more rough waters than the separate drilling barge. However, when the transport takes place along more calm waterways it may be preferred to tow the drilling barge and the larger vessel separately, and if the waterways are so narrow that the larger vessel is not allowed to pass as a separate unit, the larger vessel may be divided longitudinally into two separate sub-vessels so as to allow transportation of the vessel on rivers and other narrow waterways, the sub-vessels being subsequently reunited to re-establish said vessel, whereupon the drilling barge may be lifted or pulled into position on top of the large vessel so as to establish the combined drilling vessel, which may then be put into operation. The sub-vessels may advantageously be reunited by pulling them together by means of wires and associated drawing equipment, such as anchor winches, bollards and other standard marine equipment arranged on these sub-vessels.
The drilling barge may later again be disconnected from the larger vessel and used separately at said second drilling site, when the height or depth of the water body does no exceed a predetermined low value, and where larger waves do not occur.
The larger vessel does not function only as a support or base for the drilling barge, but the space on deck of the larger vessel not occupied by the drilling barge may be used for several other useful purposes in support of the activities performed by the equipment on the drilling barge. As examples such space may be used for personnel accommodation storage area and/or workshop area, etc. to support various offshore operations.
The method according to the invention may be used in connection with drilling and related activities, including activities in connection with the preparation, operation and service of production wells. Thus, as an example, the combined drilling barge and larger vessel may be used for assembling and laying a pipeline on the seabed below the body of water, pipe lengths from the storage area being interconnected at the workshop area so as to form a pipeline, which is gradually immersed into the body of water as it is being formed. Preferably, when the pipeline is being immersed it may pass through a tensioning system suspended in the derrick of the drilling barge.
The present invention further provides a drilling vessel comprising a drilling barge having a derrick and associated drilling equipment, and a larger supporting floatable vessel, which is adapted to receive the drilling barge on its upper deck in a position in which the drilling barge part carrying the derrick extends beyond the deck of the supporting vessel, means being provided for interconnecting the drilling barge and the supporting vessel in said position. The drilling vessel, which may, for example, be used in carrying out the method according to the invention, and the drilling vessel may be constructed and equipped as described above. Furthermore, the larger vessel may comprise towing or pulling means for towing or pulling the drilling barge into position on the deck of the larger vessel as described above.
The drilling vessel may comprise means for anchoring the supporting vessel in relation to the seabed. Such anchoring may comprise mooring lines of known types. Alternatively or additionally, the anchoring means may comprise means for submerging the supporting vessel so as to position said vessel in contact with the seabed. Such submerging means may comprise one or more water tanks or chambers within the supporting vessel and means, such as pumps, for selectively letting water into the tank or tanks and for removing water from the tanks.
The drilling vessel may comprise supporting spacing means arranged between the drilling barge and the supporting vessel, so as to position the drilling barge and the drilling equipment thereon in a desired position in relation to the seabed, and such spacing means may comprise hydraulic rams or jacks for adjusting the height of the drilling barge and of the derrick positioned thereon.
The supporting vessel may advantageously be divided longitudinally into two separate sub-vessels, so as to allow transportation of the vessel on rivers and other narrow waterways. The supporting vessel may be an existing conventional vessel or large barge, which has been cut longitudinally into two separate parts being reconstructed so as to form two individually floatable vessels. These sub-vessels are then provided with connection means, which are preferably releasable. These connection means may comprise wire-pulling means being mounted on the sub-vessels for pulling the sub-vessels together. Thus, the sub-vessels may be reunited and form a combined supporting vessel without any requirement for docking or support from a shipyard.
According to another aspect, the present invention relates to a use of a floatable vessel for carrying or supporting a smaller drilling barge, while the drilling barge is being used for performing drilling operations. The larger supporting vessel may be floating when the drilling equipment on the drilling barge is operating. However, when permitted by the conditions at the drilling site the larger vessel is preferably submerged.
According to a further aspect the present invention provides a method of establishing and/or operating a bore well in a bed or floor under a body of water at a selected location of operation by means of a drilling barge or vessel having a derrick or rig and associated drilling equipment, said method comprising: providing a plurality of separate, floatable sub-vessels at a first location remote to the selected location of operation, towing the sub-vessels from the remote first location to a second location adjacent to or closer to the selected location of operation, interconnecting the sub-vessels at said second location so as to form a barge, mounting the derrick or rig and associated drilling equipment on the barge thus formed, moving the drilling barge to the selected location of operation, and anchoring the drilling barge in relation to the bed or floor under said body of water so as to substantially align the derrick with the existing or planned bore well.
Thus, instead of positioning a smaller drilling barge on top of a larger barge as explained above, a drilling rig or a derrick and associated drilling equipment may be mounted directly on the deck of the larger barge, which is divided into interconnect able sections or sub-vessels. Thus, the drilling barge may be produced in a shipyard at a location far away from the place where the drilling barge is to be used. The floatable sub-vessels may then be towed or transported otherwise to a location, where the sub-vessels may be assembled to form a barge. The assembling is preferably performed at or close to the location at which the drilling barge is to be used.
The size and dimensions of the sub-vessels may be chosen depending on the intended means of transportation to the location of operation of the drilling barge. As an example, the size and dimensions of the sub-vessels may be chosen so as to allow towing or tugging of the sub-vessels on rivers and other narrow waterways by means of a tugboat
The sub-vessels being interconnected preferably comprise a number of elongated first sub-vessels arranged in side-by-side relationship and extending in the longitudinal direction of the barge. In order to further strengthen such structure the sub-vessels may further comprise a pair of second sub-vessels being arranged fore and aft, respectively, at the ends of the first sub-vessels so as to extend transversely to the first sub-vessels.
The sub-vessels are preferably at least partly floating when they are being assembled. Therefore, as an initial step they may be drawn together by means of drawing equipment, which may or may not be associated with the sub-vessels, such as winches, hydraulic cylinders, etc., and subsequently temporarily interconnected by mechanical interlocking means, such as books latches, or the like. When such an interim interconnection has taken place the sub-vessels may be interconnected more permanently, for example by welding. Each pair of adjacent sub-vessels are preferably welded together adjacent to the deck level and adjacent to the bottom level, respectively. In order to facilitate the welding operation the adjacent sub-vessels are preferably mutually spaced in their said temporarily interconnected condition. This may, for example, be obtained by means of connecting flanges, which are formed on and extend outwardly from the sub-vessels so as to bridge said spacing, whereby the flanges may function as spacing means. The lowermost flanges are preferably positioned above the water level allowing a person to move within the space defined between adjacent sub-vessels and to weld each flange on one sub-vessel to the adjacent sub-vessel. Thereby the sub-vessels may be permanently interconnected by dry welds within the protected area formed by the space between the adjacent sub-vessels.
The rig or derrick used on the drilling barge according to the invention may be of any suitable type, such as the usual land-based type. The rig and other necessary drilling equipment may be disassembled to an extent allowing the desired manner of transportation, such as by land, sea and/or river, to the place where the drilling barge is to be assembled. Alternatively, however, the rig or derrick may be mounted on the barge by arranging a smaller drilling barge comprising such rig or derrick and associated drilling equipment on the deck of the larger barge. Thereby an existing small drilling barge may be used in combination with a larger barge being composed by a number of sub-vessels as explained above.
When the drilling barge has completed its mission and is to be used at another remote drilling site, the more permanent interconnections or welds between adjacent sub-vessels may be cut or separated so as to divide the barge into said sub-vessels. Thereafter, the sub-vessels may be towed along rivers or other narrow waterways to the new site of operation.
The present invention further provides a drilling barge comprising: a plurality of separately floatable, sub-vessels having tanks formed therein, each sub-vessel having connecting means for interconnecting the sub-vessels in a floating condition and each sub-vessel defining a deck part and a bottom part forming in the interconnected condition of the sub-vessels the deck and the bottom, respectively, of the barge, and a drilling rig or derrick to be mounted on the deck of the barge.
The rig or derrick may be positioned at the aft part of the barge so as to extend beyond the outer limits of the barge. In the preferred embodiment, however, the rig or derrick is positioned above and in alignment with a through opening or cutout defined in the barge. The barge may further comprise all accessories necessary for performing drilling operations and/or production of petroleum products, whereby drilling operations and oil production is possible also in very remote areas where support and supplies can not be obtained easily.